Another brutal video from crisis this time -- to show captured Syrian soldiers some 150. Of them stick to their underwear forced to march across the desert. After -- is to control of the air base they were defending. A short while after the video shows them lying dead. The apparent victims of -- mass execution it was just last week that -- stunned the world with the gruesome video of the execution of American journalist James Foley. The executioner in that video identified as a British national. In London today authorities raised the terror level in the UK from substantial. To severe. He's -- -- and deeper threat to -- security. -- we have known the full. One of America's closest allies the British say they support airstrikes against -- in Iraq. But like President Obama prime minister David Cameron did not go so far as calling for air strikes in Syria. President Obama himself is trying to tamp down the emotional response to the ice -- threat. Stressing during a briefing at the white house on Thursday that developing a strategy for dealing with the terror group will take time I don't want to put the -- Before the -- we don't have a strategy. Yet a stark admission since the -- -- crisis has increased at an astonishing rate in the last year as the groups seized large areas in Iraq and Syria. The only execution prompted the president earlier this week to authorize surveillance flights over Syria group like crisis. Is beyond the pale. Along with the British the president is trying to build a coalition of allies including countries in the Middle East to confront crisis. And that will take some patients he says. -- -- the ABC news Washington.

This transcript has been automatically generated and may not be 100% accurate.

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